Summer’s officially here! Longest day in the Northern Hemisphere is June 21st. Technically, the summer solstice occurs when the sun is directly over the imaginary Tropic of Cancer, or 23.5°N latitude. It’s also known as the northern solstice because it occurs when the sun is directly over the Tropic of Cancer in the Northern Hemisphere. This year, it occurred at 9:02 am IST on June 21st.Zenith Furthest Away from the Equator. A solstice happens when the sun’s zenith is at its furthest point from the equator. On the June solstice, it reaches its northernmost point and the Earth’s North Pole tilts directly towards the sun, at about 23.4 degrees.
“Solstice” (Latin: “solstitium”) means sun-stopping. The point on the horizon where the sun appears to rise and set, stops and reverses direction after this day. On the solstice, the sun does not rise precisely in the east, but rises to the north of east and sets to the north of west, meaning it’s visible in the sky for a longer period of time. Although the June solstice marks the first day of astronomical summer, it’s more common to use meteorological definitions of seasons, making the solstice midsummer or midwinter.
Solstices in Culture
Over the centuries, the June solstice has inspired countless festivals, midsummer celebrations and religious holidays. One of the world’s oldest evidence of the summer solstice’s importance in culture is Stonehenge in England, a megalithic structure which clearly marks the moment of the June solstice. In the Southern Hemisphere, where the June solstice is known as the shortest day of the year, it marks the first day of astronomical winter, but the middle of winter in meteorological terms.
Midnight Sun or Polar Night?
On the other side of the planet, south of the Antarctic Circle there’s Polar Night, meaning no Sunlight at all, on the June solstice.
Solstice Dates Vary
Even though most people consider June 21 as the date of the June solstice, it can happen anytime between June 20 and June 22, depending on which time zone you’re in. June 22 solstices are rare – the last June 22 solstice in UTC time took place in 1975 and there won’t be another one until 2203. The varying dates of the solstice are mainly due to the calendar system – most western countries use the Gregorian calendar which has 365 days in a normal year and 366 days in a Leap Year.
A tropical year is the time it takes the Earth to orbit once around the Sun. It is around 365.242199 days long, but varies slightly from year to year because of the influence of other planets. The exact orbital and daily rotational motion of the Earth, such as the “wobble” in the Earth’s axis (precession of the equinoxes), also contributes to the changing solstice dates. The 23.4° tilt in the Earth’s axis causes varying amounts of sunlight to reach different regions during its year-long orbit around the Sun. Today, the North Pole is tipped more towards the Sun than on any other day of the year. However, that does not mean more heat or that the Earth is any closer to the Sun, per common misconceptions.
Summer solstices happen twice each year (once in each hemisphere). Summer solstice for the Northern Hemisphere = Winter solstice for the Southern Hemisphere, and vice-versa. Also, during Equinoxes (vernal and autumnal), the Sun shines directly on the Equator and the length of day and night are nearly equal in either hemisphere. More key dates for 2021 (Northern Hemisphere): Autumn Equinox: Thursday, September 23, Winter Solstice: Tuesday, December 21.